Brass plating



July 27 1954 L. R. wEsTBRooK ETAL 2,584,937

BRASS PLATING 3 Sheets-Sheet l Filed Jan. 25 1951 @ov w 7 6 s wowgmww Patented July 27, 1954 BRASS PLATING Leon R. Westbrook, Solon, and Edward J. Roehl, Warren, hio, assignors, by mesne assignments, to Pittsburgh Steel Company, a corporation of Pennsylvania Application January 25, 1951, Serial No. 207,704

24 claims.

This invention relates to the electroplating of brass from cyanide solutions and has for its object electrodepositing brass at very fast rates from high concentration solutions of high efficiency at high current densities and high temperatures, particularly on continuous steel strip. By brass is meant the common alloy comprising about 80% (range 65-8570) copper, balance zinc, and generally referred to as yellow brass.

More specific objects of the invention include the maintenance of high electrode efticiencies, and substantially constant bath composition and operating conditions with a minimum of control.

Still another object of the invention is providing an improved dry mix which may be utilized for the preparation of brass plating solutions.

Other and further objects, features and advantages of the invention will become apparent as the description proceeds.

In carrying out the invention in accordance with a preferred form thereof, We utilize a brass plating bath comprising an aqueous solution of sodium cyanide, copper cyanide, sodium hydroxide and zinc oxide with a very small proportion of zinc to copper. The proportion of sodium cyanide to copper cyanide may be relatively small, preferably a mol ratio of about 2 to 1, and the sodium hydroxide concentration is relatively very high.

A better understanding of the invention will be aorded by the following detailed description considered in conjunction with accompanying drawings and its scope Will be set forth in the claims.

In the accompanying drawing,

Fig. l is a graph of deposit composition plotted for two different temperatures, the vertical coordinate representing percent copper in the deposit and the horizontal coordinate representing cathode current density in amperes per square foot.

2 is a graph of cathode metal current eliciency plotted against cathode current density for four different temperatures.

Fig. 3 is a graph of cathode efficiency plotted against excess sodium cyanide concentration for different cathode current densities.

Fig. 4 is a graph of deposit composition plotted against excess sodium cyanide concentration, and

Fig. 5 is a graph of anode voltage plotted against anode current density for dii'rerent temperatures.

In the past, brass has been commercially plated from an aqueous solution containing copper cyanide, zinc cyanide and sodium cyanide. These are the essential ingredients, besides which the solution usually contains Various amounts of sodium carbonate and a little ammonia, either added as such or resulting from the decomposition of cyanide. There are innumerable published formulae for yellow brass plating baths. Most oi them involve dilute solutions and operate at very low current densities and relatively low eiciencies. Practically all of them have one or more of the following relationships in common:

1. The copper-zinc concentration ratio is approximately the same as in the deposit, usually from 2:1 to 4:1.

2. Sodium hydroxide is seldom present and, if it is, the concentration is very low, oi the order of about one ounce per gallon or less.

3. The sodium cyanide concentration is in definite excess of that required to form the complexes NazCLuCN) s (mol ratio NaCN/CuCN=2 1) and NazZn CN 4- This excess is commonly referred to as free cyanide.

In some formulations the sodium cyanide concentration is sumcient or in excess of the amount required to form the complexes Na3Cu CN 4 (mol ratio NaCN/CuCN=3:1) and Na2Zn(CN)4. In fact, in prior art yellow brass bath formulations the higher the concentration of free sodium cyanide, the easier it is to get good color brass deposits, but unfortunately the einciency of metal deposition decreases rapidly with increase in free cyanide concentration, and this eiiect is magniied with increase in cathode current density. The eiiciency of metal deposition is commonly referred to as cathode metal current efliciency.

Commercial brass plating is notoriously slow by reason of low cathode metal current eiciencies, of the order of or usually much less, and low operating cathode current densities, of the order of 3-10 amperes per square foot. This is the principal reason why it is not used more widely for decorative purposes and why commercial decorative brass plate over steel is so thin, around 0.00G02-0-0001 inch, that it does not last much longer than the lacquer which covers it. Numerous attempts have been made to improve the speed of brass plating baths through higher operating current densities and eiiiciencies, principally by increasing bath concentration, holding the free sodium cyanide concentration as low as possible and operating at high pI-Iby maintaining a low and carefully controlled concentration of sodium hydroxide, all of which must be held within lnarrow limits in order to consistently produce satisfactory color and composition of deposit. None of these attempts has been commercially successful because, as cathode metal current eiciency improves, the limits within which the various factors oi solution composition must be controlled rapidly become narrower, particularly with increase in cathode current density, so that a compromise must be struck between a practical degree oi control oi bath composition and operating conditions, and bath eiciency. Practically, it has not been found commercially expedient to control bath composition closely enough to get the benefits of higher '2 u* efficiencies, and higher current densities because of the degree of improvement obtainable did not warrant the added costs of control.

Another difficulty in the operation of brass plating baths has revolved around the tendency of brass anodes to polarize at relatively low current densities, usually above around five amperes per square foot, thus requiring higher voltages to force the current through the polarization film which, of course, resulted in a corresponding increase in cell voltage demand. When operated at current densities below that at which they polarize, brass anodes dissolve at around 100% metal current efficiency. Since the efficiency of deposition in commercial baths is usually much lower than 100%, the result is a buildup of metal concentration in the bath, a depletion of free cyanide, and the formation of sodium hydroxide. The net result is to throw the solution out of balance and require continuous addition of chemicals to maintain constant composition, One means to counteract this effect is the partial use of inert anodes, but this is objectionable because inert anodes accelerate the rate of sodium cyanide consumption by oxidation to result in undesirable increase in concentration of sodium carbonate which must eventually be removed.

Another suggested remedy is to provide two or three times as much anode surface as cathode so that the anode current density will of necessity be one-half or one-third that of the cathode. This is all very Well on paper, but in practice it is often impossible to meet these conditions. In the continuous plating of strip steel, for example, when a continuous strip of steel moves over or between anode beds it is practically impossible to deviate very far from a 1:1 anode and cathode surface ratio. In fact, it is generally desirable to have less anode surface than cathode so as to avoid burned deposits on the edge of the strip which results from excessively high current densities on the edges if the anode beds extend beyond the width of the strip.

On the other hand, polarization of the anodes interferes with their dissolution and throws the solution off balance in the opposite direction, since if the anode metal emciency is less than cathode metal efficiency the metal content of the bath is depleted, excess sodium cyanide is formed if caustic is present; if not, hydrogen cyanide is formed and oxygen set free at the anode, some of which reacts to oxidize cyanide, with resultant formation of undesirable carbonates.

It is therefore apparent that for steady operation at relatively constant solution composition, which is required to maintain constant deposit composition and color, the anode and cathode emciencies should be essentially equal without anode polarization, which means that the cathode eficiency should be as high as possible, preferably approaching 100%. Maximum rate of deposition requires baths that can be operated to maintain high cathode metal current eiiciencies at high current densities.

We have now found that all of the foregoing desirable objectives can be attained by the use of our new bath formulation based on a radically new concept of composition and operation. Our preferred bath comprises a high concentration, high eciency composition containing copper cyanide plus sodium cyanide essentially in proportion to form the complex Na2Cu(CN)3 mol ratio NaCN/CuCN=2:1) plus sodium hydroxide in appreciable amounts to give high conductivity, plus a very low concentration of zinc, preferably added 4 in the form of zinc oxide. A typical bath formulation, with preferred ranges and practical operating limits would be:

Table i Y. Ayrparfoxi- Approxi Algjarem- Constituent (ptimum Pgled OPractical omposiperating tion Range i Rar-.gc Sodium cyanide oz./gal 14. 5 12-18 l 9-22 Copper cyanide oa/gal.. 12.0 10-14 l 8-16 Sodium hydroxide otr/gal. 8. 0 6-10 3-16 Zinc o:-;irle.. algal.. 0.7 0.4-1.2 i 0.2-1.4 Excess NaCN on/gal. 1.2 0. 5-2. 5 I 0.5-5.0 Ratio copper metal to zinc 1 metal io solution l5 20-10 35-10 In making up plating baths according to the above formulation, we prefer to prepare two separate solutions and mix them rather than try to dissolve all the chemicals at once. First dissolve the sodium hydroxide and then the zinc oxide on about one-third the final volume of water. Next dissolve the sodium cyanide and the copper cyanide in a like volume of water. Then mix the two solutions and add water to make the required nal volume.

Of course zinc cyanide or other cyanide soluble compound of zinc can be used instead of zinc oxide in preparing our oath formulations, making due allowance in balancing the constituents used so that the desired bath composition results. For example, our preferred bath formulation may be prepared by dissolving in water the following chemicals in the order named:

(Ja/gal. Sodium cyanide 13.7 Copper cyanide 12.0 Zinc cyanide 1.o Sodium hydroxide 8.0

If desired, the solution may also be prepared from a dry mix instead of dissolving ingredients successively as we have just explained.

When it is desired to ship the ingredients to plants where the operators are not equipped or sufficiently familiar with the principles involved to measure out the ingredients in the best proportions, a dry mix may be furnished. Thus, if it is desired to supply a single dry mix for producing the approximate optimum composition set forth in the table, the dry mix may consist of ingredients in the following proportions: 14.5 ounces sodium cyanide, l2 ounces copper cyanide, 8 ounces sodium hydroxide and 0.7 ounce zinc oxide. An equivalent dry mix can be made by mixing the following ingredients in the proportions shown:

Per cent Sodium cyanide 4o Copper cyanide 34 Zinc cyanide 3 Sodium hydroxide 23 Per cent NaCN 52 CuCN 44.5 ZntCN)2 3.5

' The preferred composition bath can then be made ing, or treatment with 0.05 oz./gal. of sodium sulde followed by several hours standing then charcoal treatment and filtration. Such purification treatments are highly recommended because of the presence of impurities in commercial copper cyanide, zinc cyanide and lsine oxide. 'Freshly made baths, whether purified or not, usually produce a multicolored film over the deposit for the first few hours oi operation. Purification reduces the time during which filmed deposits are produced. These films, which are 'believed to be due to impurities in the bath, may be almost any color but are usually a dark, reddish brown and form over the surface of the deposit. These films are not always obtained with purified fresh baths, but if and when formed, they are merely a transitory phenomenon. They can easily be removed from the surface of the deposits by brushing or puffing, after which the deposits will be found to be of satisfactory color. Another means of removing the film is to dip the plate for a few seconds in a dilute solution of chromic acid, around 0.25 ounce per gallon in concentration at room temperature or slightly above. After a short time of bath operation the film formation gradually disappears, after which deposits of good color and luster are obtained.

Our preferred new bath formulation differs from all prior art compositions for yellow brass deposition in the following particulars:

(l) The molal ratio of NaCN to CuCN is essentially 2:1, no NaCN being required for the zinc content, which is preferably in the form of sodium zincate (Zinc oxide dissolved in sodium hydroxide).

(2) a. The caustic soda or sodium hydroxide concentration is relatively very high-several ounces per gallon instead of around one or less, or none. b. The concentration of sodium hydroxide is not significant within the range of about 6-10 ounces per gallon. These relatively high concentrations are very desirable from the standpoint of providing high bath conductivity and high electrode eiciencies.

(3) The copper-zinc ratio is exceptionally high, normally of the order of around :1 instead of around 3:1 as in present day commercial baths.

(4) The color of the deposit and its composition is controlled principally by holding the zinc concentration within relatively wide limits rather than by carefully controlling free cyanide, pl-l, or caustic concentration, as is done with prior art baths. None of these factors is critical in the operation of our new bath.

As noted above, the principal control is the zinc concentration in the bath. ln practical operation this factor holds surprisingly constant. This is because the deposit composition holds relatively constant over a wide range of operating conditions, remaining usually within the approximate range of 'l5-80% Cu, the cathode metal current efliciency remains high over a wide range of operating conditions, and the anodes do not polarize at anode current densities below 'I0-100 amperes per square foot, depending on bath composition and temperature. Thus, by holding the average anode composition essentially the same as the deposit composition, that is of copper content between 'l5-80%, the bath composition is automatically kept relatively constant. Thus, the absence of anode polarization permits anode and cathode eiliciencies to approach equality. This condition is always desirable since the bath then acts as a relatively constant composition carrier of metal. Agitation helps maintain bath equilibrium, as does movement of the cathode, as in continuous steel strip plating for example. 1f the zinc concentration of the bath wanders, it may be adjusted by adding anodes higher or lower in cinc content as required. Variation, if any, is at such a slow rate that routine control analysis of either bath or deposit `/vill provide information regarding trends that can be used as a basis for such adjustments as may be found necessary. The bath operates best at around 185 F. or through a range of 16E-200 F. and at current densities of 25-150 amperes per square foot, preferably at around A/SF where the cathode current efliciency is around 90% or better. The current densities are about the same at anode and cathode, since, as previously pointed out, in practice there is little deviation from 1:1 anode to cathode surface ratio.

The higher operating temperatures are accompanied by high erliciences, high bath conductivity, less anode polarization, and wider permissible operating limits in zinc concentration. In other words, as the bath temperature is raised from F. to 200 F'., a gradual improvement in uniformity of operating conditions and deposit appearance and composition under variations in current density are noted, and the rate of these improvements is accelerated with rise in temperature. The practical operating temperature may be selected to best suit the conditions encountered in any installation.

The relationships between the common operating variables are shown graphically in Figs. l to 5, inclusive.

Fig. 1 represents the variation of deposit coinposition with cathode current density at tempel'- atures between 150 F. and 200 F. The curves in this graph are based on a bath composition as follows; 14.5 ounces sodium cyanide, l2 ounces copper cyanide, 0.7 ounce Zinc oxide, 8.0 ounces sodium hydroxide, excess sodium cyanide 0.5 to 1.2 ounces per gallon. The two curves in Fig. 1 are plotted for bath temperatures of 200 F. and 150 F., respectively, the upper curve being for the higher temperature. The curves show that between 25 and 150 amperes per square foot cathode current density and between 15G-200 F. the cathode composition averages around 50% Cu, varying only from about 'Z5-83% Cu.

Fig. 2 depicts the relationships between cathode current density and cathode metal current eiTlciency at various temperatures. It shows that between -200o F. and between 20-120 amperes per square foot cathode current density, the cathode metal current eiiiciency averages better than 90%, varying between about 'T8-98%. It is particularly noteworthy that high cathode metal current eiciency is maintained at high current densities and high bath temperatures, i. e., it is above 90% at 10.0 amperes per square foot at bath temperatures above 180 F. rlhis is particularly important in providing rapid plating rates and maintaining constancy of bath composition. It will be noted that the line representing relationships at 150 F. lies below the above ranges which apply to the other lines. While our new bath is essentially a high temperature, high current density bath and the full benefits of the many advantages of our new bath are -best realized at the higher temperatures, it is still better than any prior art baths at lower temperatures such at 150 F. and, if operating conditions prohibit higher temperatures, the bath can be operated to good advantage at lower temperatures. For this reason data obtained at the lower temperature are included. The bath compositions ior Fig. 2 are the same as specified for Fig. 1. The four curves plotted in Fig. 2 are based on four different bath temperatures, namely 150 F., 165 F., 180 F. and 200 F., the uppermost curve being for the highest temperature.

Fig. 3 represents the relationship between excess sodium cyanide (over a 2:1 ratio of NaCN/CuCN), and cathode metal current efiiciency at various cathode current densities and at 165 F. Fig. 3 is based on a bath composition of copper cyanide 12 ounces per gallon, zinc oxide 0.7 ounce per gallon, sodium hydroxide 8 ounces per gallon, with the excess sodium cyanide being varied as shown by the curves. The curves are plotted for four different cathode current densities 27, 57, 86 and 120 amperes per square foot respectively, the uppermost curve being for the lowest current density. Fig. 3 shows that this excess sodium cyanide, which is generally referred to in the prior art as free cyanide, is not a critical factor in the operation of our new bath, since within the lower range of 0.5-5.0 ounces per gallon, within which control is extremely easy, the variation has very little eiect on eiciency. This lack of effect is even less at higher temperatures, and is of great importance from the standpoint of providing high and relatively constant plating rates and maintaining relatively constant bath composition. This is one of the very important aspects in which our new brass plating process is superior to prior art processes. While of course, our bath can be operated with excess of free cyanide concentrations in excess of 5 oz./gal., as shown in Fig. 3, it is obvious therefrom that the efficiency falls on at a rate which increases with increased free cyanide concentration and, therefore, such procedure is not desirable, especially since there are no compensating advantages to be gained thereby.

Fig. 4 consists of two curves bounding an area showing the relationship between percentage copper in the deposit and excess sodium cyanide in ounces per gallon in the bath over a range of zinc concentrations of 0.5-1.0 ounce per gallon of zinc oxide at 165 F., with the bath composition as follows; 12 ounces per gallon of sodium cyanide, 8 ounces per gallon of sodium hydroxide, 0.5 to 1.0 ounce per gallon of zinc oxide, utilizing a cathode current density of 120 amperes per square foot. The cross-hatched area between the upper and lower curves falling within the range of Gil-85% copper in the deposit represents the good color range. Fig. a emphasizes the wide range of bath composition over which yellow brass deposits f satisfactory color and composition can be obtained. This is important from a commercial operating standpoint in maintaining a satisfactory product despite variations in bath composition, since it avoids the necessity for frequent analyses and adjustment, and assures continuity of uniform production with elimination of off quality material. This is another important aspect in which our new bath is greatly superior to prior art baths.

Fig. consists of curves at four different temperatures, 150 F., 165 F., 180 F. and 200 F.,

respectively, as shown from left to right, of anode voltage plotted against anode current density in amperes per square foot for the same bath composition as Figures 1 and 2. The graph shows the relationship between anode polarization voltages and anode current densities at various temperatures in baths without agitation. From this ngure it is evident that the anodes do not polarze until current densities of '70-90 amperes per square foot are reached, depending on temperature. This greatly marked improvement over prior art baths and processes, in which 5 amperes per square foot is the nominal limit in unagitated baths, constitutes another very important advantage of our invention. Anode polarization and its resultant disastrous effects on bath operation as previously discussed has been one of the most troublesome factors in prior art baths. For the irst time we have been able to operate unagitated commercial brass baths at anode current densities up to around amperes per square foot without polarization. This one factor alone is sufcient to constitute inventive improvement over the prior art. Bath agitation of course raises the upper limit of current density before polarization occurs, the extent of the rise depending on the degree of agitation. Anode current densities of around amperes per square foot have been attained with moderate agitation, and Without polarization. As previously mentioned the best operation is obtained with anode current density exceeding 25 amperes per square foot.

Figs. 1 and 5 emphasize the outstanding features of our invention, particularly the fact that it provides relatively high concentration baths that operate at high temperatures, high current densities, at high eiciencies and without anode polarization under these conditions. Our new bath formulation produces yellow brass deposits of good color and relatively constant composition under a wide variety of operating conditions, and maintains itself well within optimum operational limits with a minimum of control. In essence, our new bath is a high speed plating bath, comparable in operating speed, efficiency and econ- @my with modern baths for plating other common metals such as copper, nickel, cadmium. zinc, tin, etc. Our new bath, for the first time, puts brass plating on a par with these other metals commercially.

En addition to the beiorementioned advantages resulting from our new bath formulation, the following corollary advantages have been found in practice.

(1) Because of the low 2:1 ratio of sodium cyanide to copper cyanide, the cyanide losses due to hydrolysis and oxidation are greatly diminished, since these destructive forces attack mainly the NaCN over and above that required for the complex NaaCuNg. Thus advantage can be taken of the desirable high temperature operating characteristics of the bath without suiering undue cyanide losses.

(2) Another advantage of the much lower rate of cyanide decomposition is of course the corresponding decrease in rate of carbonate formation with resultant lowering of the frequency with which sodium carbonate must be removed by the conventional methods of freezing out or chemical treatment. This is always a costly nuisance at best, and if not carefully done may result in solution losses.

(3) Because the anode and cathode eiiiciencies are essentially equal under operating conditions the bath composition remains relatively constant, thus eliminating the necessity of adjusting composition by adding metallic salts as is commonly done in prior art operations. Zinc and copper cost more as cyanides than as metals, on an equivalent basis.

While the foregoing disclosures have been based on sodium compounds, i. e., sodium hydroxide and sodium cyanide, it is of course possible to substitute the chemically equivalent amounts oi either potassium hydroxide or potassium cyanide or both in any of the above formulations. Such substitution, resultinCr in mixed sodium-potassium baths or in all potassium baths, will yield somewhat improved results over those obtained from the corresponding all sodium baths, especially at the higher current densities; but the all sodium baths are themselves so good that room for improvement is small, and in our opinion, the degree of improvement obtained from part or all potassium baths is not suflciently great to warrant the added cost. However, this is a matter of individual economics, and it is understood that the partial or complete substitution of potassium compounds for sodium compounds in our formulations are fully comprehended within our invention.

The term alkali metal is used in the claims to signify either or both of the common alkali metals sodium and potassium.

While the invention has been described as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that the invention is not limited thereto, since various modifications will suggest themselves to those skilled in the art without departing from the spirit of the invention, the scope of which is set forth in the annexed claims.

What we claim is:

l. A yellow brass plating bath comprising in aqueous solution, sodium cyanide, copper cyanide, sodium hydroxide and a cyanide soluble rinc compound, the sodium hydroxide being present in concentration exceeding 3 ozs. per gallon and the zinc being maintained in low concentration, such that the ratio of copper to zinc in solution lies between 35:1 and 10:1.

2. A yellow brass plating bath comprising in aqueous solution, sodium cyanide, copper cyanide, sodium hydroxide and a cyanide soluble zinc compound, the sodium hydroxide being present in concentration exceeding 3 ounces per gallon and the zinc being maintained in low concentration, such that the ratio of copper to zinc solution is approximately :1.

3. A yellow brass plating bath comprising in aqueous solution approximately 9 to 22 ounces per gallon sodium cyanide, 8 to 16 ounces per gallon copper cyanide, 3 to 16 ounces per gallon sodium hydroxide, 0.2 to 1.4 ounces per gallon zinc oxide.

4. A yellow brass plating bath comprising in aqueous solution approximately 12 to 18 ounces per gallon sodium cyanide, 10 to 14 ounces per gallon copper cyanide, 6 to l0 ounces per gallon sodium hydroxide, 0.4 to 1.2 ounces per gallon zinc oxide.

5. A yellow brass plating bath comprising in aqueous solution approximately 14.5 ounces per gallon of sodium cyanide, 12 ounces per gallon of copper cyanide, 8 ounces per gallon sodium hydroxide, 0.7 ounce per gallon zinc oxide.

6. In a process for the electrodeposition of yel- 10W brass the step comprising depositing brass 10 from an aqueous solution containing sodium cyanide, copper cyanide, sodium hydroxide and a cyanide soluble zinc compound, the sodium hydroxide being present in concentration exceeding 3 ozs. per gallon and the Zinc being maintained in low concentration, such that the ratio of copper to zinc in solution lies between 35:1 and 10:1.

7. In a process for the electrodeposition of yellow brass the step comprising depositing brass from an aqueous solution containing sodium cyanide, copper cyanide, sodium hydroxide and a cyanide soluble zinc compound, the sodium hydroxide being present in concentration exceeding 3 ounces per gallon and the zinc being maintained in low concentration, such that the ratio of copper to zinc in solution is approximately 15:1.

8. In a process for the electrodeposition of yellow brass the steps comprising depositing brass from an aqueous. solution containing approximately 9 to 22 ounces per gallon sodium cyanide, 8 to 16 ounces per gallon copper cyanide, 3 to 16 ounces per gallon sodium hydroxide, 0.2 to 1.4 ounces per gallon of zinc oxide and maintaining the solution at a temperature between approximately F. and 200 F.

9. In a process for the electrodeposition of yellow brass the steps comprising depositing brass from an aqueous solution containing approximately 12 to 18 ounces per gallon sodium cyanide, l0 to 14 ounces per gallon copper cyanide, 6 to 10 ounces per gallon sodium hydroxide, 0.4 to 1.2 ounces per gallon zinc oxide and maintaining the solution at a temperature between approximately 150 F. and 200 F.

l0. In a process for the electrodeposition of yellow brass the steps comprising depositing brass from an aqueous solution containing approximately 14.5 ounces per gallon of sodium cyanide, 12 ounces per gallon of copper cyanide, 8 ounces per gallon sodium hydroxide, 0.7 ounces per gallon zinc oxide and maintaining the solution at a temperature between approximately 150 F. and 200 F.

1l. A dry mix composition which, when dissolved in water to yield 1 gallon of solution, may be used to form a yellow brass plating bath, the proportions of ingredients in said composition being approximately within the ranges of 9 to 22 ounces of sodium cyanide, 8 to 16 ounces of copper cyanide, 3 to 16 ounces of sodium hydroxide, 0.2 to 1.4 ounces of zinc oxide per gallon of resultant solution.

l2. A dry mix composition which, when dissolved in water to yield 1 gallon of solution, may

f be used to form a yellow brass plating bath, the

proportions of ingredients in said composition being approximately Within the ranges of 12 to 18 ounces of sodium cyanide, 10 to 14 ounces of copper cyanide, 6 to 10 ounces of sodium hydroxide, 0.4 to 1.2 ounces of zinc oxide per gallon of resultant solution.

13. A dry mix composition which, when dissolved in water to yield 1 gallon of solution, may be used to form a yellow brass plating bath, the proportions of ingredients in said composition being approximately within the ranges of 14.5 ounces oi sodium cyanide, 12 ounces of copper cyanide, 8 ounces of sodium hydroxide, 0.7 ounces of zinc oxide per gallon of resultant solution.

14. A dry mix composition which, when dissolved in water in proportion to give approximately 35 ounces of dry mix composition per gallon of resultant solution, may be used to form a yellow brass plating bath, the ingredients in 1l said composition being approximately in the proportions of sodium cyanide 40%, copper cyanide 34%, Zinc cyanide 3%, sodium hydroxide 23%.

15. A dry mix composition which may be dissolved in water in the approximate proportion of 27 ounces of dry mix per gallon of resultant solution along with sodium hydroxide in the proportion of 8 ounces per gallon of resultant solution to produce a yellow brass plating bath, said dry mix comprising a mixture of chemicals in the following approximate proportions: sodium cyanide 52.0%, copper cyanide 44.5%, zinc cyanide 3.5%.

16. rI'he process of electroplating yellow brass by electrolyzing a solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble zinc compound, characterized by restricting the proportions of zinc to about 1/15 that of copper and heating the solution sufficiently to maintain its temperature between about 150 F. and 200 F.

17. The process of electroplating yellow brass by electrolyzing a solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble Zinc compound, characterized by maintaining the current density between 25 and 150 amperes per square foot, restricting the proportion of zinc to about 1/15 that of copper and heating the solution sufficiently to maintain its temperature between about 150 F. and 200 F.

18. The process of electroplating yellow brass substantially as herein set forth by electrolyzing a solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble zinc compound characterized by maintaining the cathode current density between 25-150 amperes per square foot, restricting the proportions of zinc to 1,45 that of copper and heating the solution suiiiciently to maintain its temperature between about 150c F. and 200 F., while operating with anode current densities between 25 and 100 amperes per square foot.

19. In a process for the electro-deposition of yellow brass the steps comprising depositing brass from an aqueous solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble zinc compound, maintaining the zinc in sufiiciently low concentration so that the ratio of copper to Zinc in solution lies between 35-1 and 10-1, heating the solution sufficiently to maintain its temperature between about 150 F. and 200 F., and maintaining the cathode current density between about 25 and 150 amperes per square foot.

20. In a process for the electro-deposition oi yellow brass the steps substantially as herein set forth comprising depositing brass from an aqueous solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble zinc compound, maintaining the zinc in sufficiently low concentration so that the ratio of copper to Zinc in solution lies between 35-1 and 10-1, heating the solution sufficiently to maintain its temperature between about 150 F. and 200 F., and maintaining the cathode current density between about 25 and 150 amperes per square foot, while operating with anode current densities between 25 and 100 amperes per square foot.

21. In a process for the electro-deposition of yellow brass the steps comprising depositing brass from an aqueous solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble Zinc compound, maintaining the zinc in sufficiently low concentration so that the ratio of copper to zinc in solution is approximately 15-1, heating the solution sufficiently to maintain its temperature between about F. and 200 F., and maintaining the cathode current density between about 25 and 150 amperes per square foot.

22. In process for the electro-deposition of yellow brass the steps substantially as herein set forth comprising depositing brass from an aqueous solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble zinc compound, maintaining the Zinc in sufficiently low concentration so that the ratio of copper to zinc in solution is approximately 15-1, heating the solution suiiiciently to maintain its temperature between about 150 F. and 200 F., and maintaining the cathode current density between about 25 and 150 amperes per square foot, while operating with anode current densities between 25 and 100 amperes per square foot.

23. In a process for the electrodeposition of yellow brass upon an article, the steps comprising immersing the article and a yellow brass anode, having a composition of copper and Zinc in approximately the proportions desired in the coating to be plated upon the article, in an electrolyte and passing an electric current through said electrolyte between the anode and the article, said electrolyte comprising in solution ingredients in about the following proportions, sodium cyanide 9 to 22 ounces per gallon, copper cyanide 8 to 16 ounces per gallon, sodium hydroxide 3 to 16 ounces per gallon, zinc oxide 0.2 to 1.4 ounces per gallon.

24. In a process for the electrodeposition of yellow brass upon an article, the steps comprising immersing the article and a yellow brass anode, having a composition of copper and Zinc in approximately the proportions desired in the coating to be plated upon the article, in an electrolyte and passing an electric current through said electrolyte between the anode and the article, said electrolyte comprising in solution ingredients in about the following proportions, 14.5 ounces sodium cyanide, 12 ounces copper cyanide, 8 ounces sodium hydroxide, 0.7 ounce zinc oxide.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,181,773 Wernlund Nov. 28, 1939 OTHER REFERENCES Oplinger, Metal Industry, February 3, 1939, pp. 

1. A YELLOW BRASS PLATING BATH COMPRISING IN AQUEOUS SOLUTION, SODIUM CYANIDE, COPPER CYANIDE, SODIUM HYDROXIDE AND A CYANIDE SOLUBLE ZINC COMPOUND, THE SODIUM HYDROXIDE BEING PRESENT IN CONCENTRATION EXCEEDING 3 OXS. PER GALLON AND THE ZINC BEING MAINTAINED IN LOW CONCENTRATION, 